Multi-wheel-drive vehicle with a front transaxle device

ABSTRACT

A multi-wheel-drive vehicle has at least six wheels, a transmission with a first brake, and a transaxle device for the front drive wheels. The transaxle device includes a drive axle, an input shaft rectangular to the drive axle for receiving power from the transmission, a drive train connecting the drive axle to the input shaft, a second brake, and a clutch device in the input shaft. The drive axle may be a pair of drive axles connected by a differential unit. The clutch device can selectively isolate the drive axle from the rotation of the input device. Further, the clutch device is engaged when the first brake is applied. Additionally, the first and second brakes may be connected such that their operation may be synchronized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application. Ser. No.10/810,835, filed Mar. 29, 2004 now U.S. Pat. No. 7,028,801, which is acontinuation of U.S. patent application Ser. No. 10/448,369, filed May30, 2003, now U.S. Pat. No. 6,729,992, issued May 4, 2004, which is adivisional of U.S. patent application Ser. No. 09/876,092, filed Jun. 8,2001, now U.S. Pat. No. 6,634,446, issued Oct. 21, 2003, which are allincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a front transaxle device of amulti-wheel-drive vehicle.

2. Background Art

Conventionally, a multi-wheel-drive vehicle wherein four or more wheelsare driven is known.

In this multi-wheel-drive vehicle, transaxle devices for supportingaxles are disposed corresponding to the positions of the axles. Forexample, a rear transaxle device for supporting rear axles is disposedat a rear portion of the vehicle, and a front transaxle device forsupporting front axles is disposed at a front portion of the vehicle. Ina structure where six or more wheels are driven, a middle transaxledevice for supporting middle axles is disposed at a longitudinallyintermediate portion of the vehicle.

Furthermore, a transmission which transmits the power from a prime mover(e.g., an engine) is provided. By transmitting the power from thetransmission to each of the transaxle devices, the wheels are driventhrough each of the axles.

In comparison with a two-wheel-drive structure, the above-mentionedmulti-wheel-drive structure is more useful in that its drivingperformance over a bad road is good, and plenty of power is availablefor climbing a hill. Thus, this structure has come to be widely adoptedby various kinds of vehicles such as automobiles, agricultural trucks,and the like.

Now, further improvement of such a multi-wheel-drive vehicle in terms ofits driving performance over bad roads, cost-saving, maintainability,etc., is increasingly desired given the increasing popularity of suchvehicles.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to provide a front transaxle device whichgives improved braking performance to a multi-wheel-drive vehicle so asto improve further the driving performance of the vehicle over badroads. Another object of the invention is to provide the front transaxledevice with a simple structure so as to reduce manufacturing costs andenhance the maintainability thereof.

According to the present invention, a front transaxle device provided toa multi-wheel-drive vehicle comprises an input shaft for receivingpower, a pair of left and right front axles supported in the fronttransaxle device, a differential connecting the left and right frontaxles in a differential manner, a pinion shaft, a clutch device whichengages the pinion shaft with and disengages the pinion shaft from theinput shaft, a rotary object interposed between the differential and thepinion shaft, and a brake device which brakes the rotary object.Therefore, the braking performance is improved and the vehicle's brakingdistance can be shortened. Thus, a multi-wheel-drive vehicle, which canrun smoothly on a bad road and enhance fuel economy, may be available.Furthermore, by operating the clutch device, it is easy to selectbetween the mode wherein the power is transmitted to the front wheelssupported by the front transaxle device and the mode wherein the poweris not transmitted to the front wheels. Thus, by linking the clutchdevice with operating means, a vehicle which can be put between4-wheel-drive mode and 6-wheel-drive mode (for example) is available.Additionally, because the clutch device is disposed between the inputshaft and the pinion shaft and the brake device is disposed at therotary object, the two devices are separated and can avoid interferingwith each other, thereby reducing the complexity of the layout.

The brake device comprises a piston which can be moved hydraulically,friction objects which engage with each other by the force of thepiston, and a mechanism which maintains a constant stroke of the pistonto engage the friction objects regardless of any abrasive reduction ofthe friction objects. Therefore, in spite of abrasive reduction offriction objects in the brake device, it is unnecessary to adjust thestroke of the piston to keep a good braking response of the brakedevice, thereby reducing the need for maintenance.

The rotary object is a middle shaft disposed between the pinion shaftand the differential and supported parallel to a rotational axis of thedifferential, and the middle shaft is engaged with the differentialthrough a spur gear. Therefore, the parts of the brake device arearranged along and detached from the middle shaft parallel to therotational axis of the differential. Thus, installation and removal ofthe brake device is easy, thereby resulting in good maintainability.Furthermore, because the middle shaft is connected with the differentialthrough the spur gear, realignment using a shim and the like, which isnecessary in a structure having the middle shaft connected with thedifferential through bevel gears, is not necessary. Such alignment canbe eliminated.

A front transaxle device is provided to a multi-wheel-drive vehiclewhich has six or more wheels, wherein a pair of foremost wheels of thevehicle are supported and can be driven. A transmission provided to thevehicle is connected with the front transaxle device through a clutchdevice which is engaged when a brake operating means provided to thevehicle is operated to brake. Therefore, when the brake operating meansis operated to its braking position by the linkage between the brakeoperating means and the clutch device, braking force is also transmittedto the pair of foremost wheels. Thus, the vehicle's braking distance athigh speed can be shortened. Additionally, the front transaxle devicecan be bypassed when the brake device is not being operated, therebyenhancing fuel economy.

Other and further objects, features, and advantages of the inventionwill appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a schematic diagram of a driving transmission system of amulti-wheel-drive vehicle including a front transaxle device of thepresent invention;

FIG. 2 is a horizontally sectional view of the front transaxle device;

FIG. 3 is an expanded horizontally sectional view of the front transaxledevice, showing an automatic gap alignment mechanism, wherein a pistonis located at its original brake-released position;

FIG. 4 is a sectional view of the same showing the state that the pistonis moved at a stroke of length A from the state shown in FIG. 3, andfriction discs are engaged with each other;

FIG. 5 is a sectional view of the same showing the state that the pistonis moved at a stroke of length A from its original brake-releasedposition when the friction discs are worn away;

FIG. 6 is a sectional view of the same showing the state that the pistonis moved at a stroke of length B from the state shown in FIG. 5, and thefriction discs are engaged with each other;

FIG. 7 is a sectional view of the same showing the state that the pistonis returned at a stroke of length A from the state shown in FIG. 6 toits new brake-released position;

FIG. 8 is a horizontally sectional view of a modification of the fronttransaxle device wherein the brake device is disposed onto a pinionshaft;

FIG. 9 is a hydraulic circuit diagram of a control system forcontrolling front and rear brake devices;

FIG. 10 is a hydraulic circuit diagram of a control system forcontrolling the front and rear brake devices according to anotherembodiment; and

FIG. 11 is a diagram of the embodiment shown in FIG. 10, showing thestate that a brake pedal is depressed and a clutch device linked withthe brake pedal is engaged.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a multi-wheel-drive vehicle 1 comprises a fronttransaxle device 10 disposed at its front portion, a middle transaxledevice 16 disposed at its longitudinally intermediate portion, and arear transaxle device 4 disposed at its rear portion. The fronttransaxle device 10 includes a pair of left and right front axles 11,the middle transaxle device 16 includes a pair of left and right middleaxles 25, and the rear transaxle device 4 includes a pair of left andright rear axles 8. Each of above-mentioned front, middle, and rearaxles 11, 25 and 8 supports each of front wheels 12, middle wheels 26,and rear wheels 9, respectively, at their outer ends.

A front brake device 100 which serves as a first braking device isprovided to the front transaxle device 10, and rear brake devices 22which serve as a second braking device are provided to the reartransaxle device 4.

The front wheels 12 are steerable, i.e., rotatable leftward andrightward according to manipulation of a steering operating device (notshown).

A transmission 13 is provided in the rear transaxle device 4. The powerfrom an engine 3 installed in the body of the vehicle is transferred tothe transmission 13 and changes rotational speed. Then, the power isused to drive the left and right rear wheels 9 through the rear axles 8,and also, it is transferred to the middle transaxle device 16 so as todrive the middle wheels 26 through the middle axles 25. Thus, thevehicle moves forward and backward by the driving of the rear wheels 9and the middle wheels 26, i.e., in 4-wheel-drive.

Alternatively, the power from the transmission 13 may be transferred tothe front wheels 12 so as to drive all six wheels 9, 12 and 26, therebyenabling the vehicle to be put in 6-wheel-drive. This structure will bedescribed later.

A structure of the rear transaxle device 4 will now be described.

The rear transaxle device 4 comprises a rear axle housing 31 whichhouses the transmission 13 together with the rear axles 8. An inputshaft 5 of the transmission 13 is connected to an output shaft 6 of theengine 3 through a belt-type automatically continuous variabletransmission (hereafter “CVT”) 7 comprising split pulleys and a belt.

The transmission 13 comprises a torque sensor 34 and a speed-changinggear mechanism 35. The torque sensor 34 detects torque, which is appliedon the wheels as load, and translates the torque into an output signal.The speed-changing gear mechanism 35 is operated by manipulating aspeed-changing operating device like a lever or a pedal (not shown)disposed outside the rear axle housing 31.

The rear axle housing 31 also houses a differential 32 interposedbetween the speed-changing gear mechanism 35 and the pair of left andright rear axles 8. The differential 32 connects the left and right rearaxles 8 differentially with each other. The differential 32 is providedwith a differential locking mechanism 33 in the rear axle housing 31.The differential locking mechanism 33 is linked with adifferential-locking device like a lever or a pedal (not shown) disposedoutside the rear axle housing 31 so as to lock the differential 32. Apower take-off casing 15 is fixed on a side portion of the rear axlehousing 31. The power take-off casing 15 is provided therein with apower output section from which power is transferred to the middletransaxle device 16 and the front transaxle device 10.

The above-mentioned input shaft 5 is supported laterally in the rearaxle housing 31 and projects outwardly from either the left or rightsides thereof. A follower split pulley 36 is provided on the outwardlyprojecting portion of the input shaft 5, which serves as an inputsection receiving the power from the engine 3. The output part of theCVT 7 is formed by this follower pulley 36. The CVT 7 is normally formedsuch that the speed reduction ratio is automatically steplessly reducedaccording to the increase of rotary speed of the engine 3.

In the rear axle housing 31, a main shaft 37 is provided coaxially withthe input shaft 5. The main shaft 37 and the input shaft 5 are connectedwith each other through above-mentioned torque sensor 34. The torquesensor 34 detects various type resistances such as rolling resistance,air resistance, acceleration resistance, and grade resistance generatedfrom each of the driven wheels, and outputs detection signals into acontroller (not shown). The controller adjusts the degree of opening ofa throttle valve of the engine 3 corresponding to the detection signals,thereby serving as a torque sensing governor.

In the rear axle housing 31, a counter shaft 41 is disposed parallel tothe main shaft 37. The speed-changing gear mechanism 35 is providedbetween both shafts 37 and 41.

The speed-changing gear mechanism 35 comprises a plurality of (in thisembodiment, two) drive gears fixed on the main shaft 37 to rotatetogether with the main shaft 37, and a plurality of (in this embodiment,two) transmission gears supported rotatably on the counter shaft 41 toengage with the respective drive gears on the main shaft 37, therebyproviding various (in this embodiment, two, i.e., high and low) gearratios. In order to reverse the rotational direction of the countershaft 41 while the main shaft 37 is rotated in a fixed direction, thespeed-changing gear mechanism 35 also comprises a driving reverse gearfixed on the main shaft 37, a reverse gear supported rotatably on thecounter shaft 41, and an idle gear through which both the reverse gearson the shafts 37 and 41 engage with each other.

A gear-changing clutch slider 47 is axially slidably but not relativelyrotatably fitted onto the counter shaft 41 through a spline. By slidingthe gear-changing clutch slider 47, one gear is selected from among thetwo transmission gears and the reverse gear on the counter shaft 41 toengage with the counter shaft 41 through the gear-changing clutch slider47. This selection brings the counter shaft 41 into a high-speedregularly directed rotation, a low-speed regularly directed rotation, ora reversely directed rotation depending upon which gear is chosen. Also,the gear-changing clutch slider 47 can be located at its neutralposition where it engages with none of the gears. The gear-changingclutch slider 47 is linked with the above-mentioned speed-changingdevice (not shown).

The counter shaft 41 is fixedly provided thereon with an output gear 51adjacent to one of its ends, thereby transmitting the rotation of thecounter shaft 41 to the above-mentioned differential 32.

The differential 32 generally uses bevel gears to connect the left andright rear axles 8 in a differential manner. An input gear 53 isdisposed on a differential casing, which houses the bevel gears, so asto engage with the output gear 51. The differential locking mechanism 33is disposed around one of the axles 8 so as to engage the differentialcasing with and disengage the differential casing from the axle 8according to operation of the differential locking lever (not shown).When the differential casing engages with the axle 8, both the axles 8are locked together, i.e., the differential 32 is locked.

The rear brake devices 22 are provided respectively on the pair of leftand right rear axles 8 so as to apply brake force onto both rear axles 8according to the operation of a later-discussed brake pedal.

One end of the counter shaft 41 extends toward one of the left or rightsides into the power take-off case 15, and a bevel gear 62 is fixed ontoits end portion. An output shaft 63 is supported in the longitudinaldirection of the vehicle and perpendicularly to the counter shaft 41 inthe power take-off case 15. A bevel gear 64 is fixed onto the outputshaft 63 and engages with the bevel gear 62.

The output shaft 63 projects forward from the power take-off case 15,and connects to a transmission shaft 87 of the middle transaxle device16 through a drive shaft 17.

Next, the middle transaxle device 16 will be described.

The transmission shaft 87 is supported in the longitudinal direction ofthe vehicle, and its rear end projects rearward so as to receive drivingforce from the rear transaxle device 4. The transmission shaft 87 alsoprojects forward from the middle transaxle device 16, thereby forming anoutput section for the front transaxle device 10.

A middle-axle drive gear 86 is fixed onto the transmission shaft 87, anda middle shaft 83 is rotatably supported parallel to the transmissionshaft 87. An intervention gear 84 is fixed onto one end of the middleshaft 83 so as to engage with the middle-axle drive gear 86, and a bevelgear 85 is provided onto the other end of the middle shaft 83. The bevelgear 85 engages with an input bevel gear 90 of a differential 89 whichdifferentially connects the left and right middle axles 25 with eachother.

Next, the structure of the front transaxle device 10 will be describedin accordance with FIGS. 1 and 2.

In the front transaxle device 10, an input shaft 14 is rotatablysupported by a housing 88, and connects with the transmission shaft 87of the middle transaxle device 16 through a propeller shaft 18,universal joints, and the like.

In the housing 88, a pinion shaft 95 is disposed forward of the inputshaft 14 and supported coaxially with the input shaft 14. A bevel gear97 is fixed onto one end portion of the pinion shaft 95. The input shaft14 is notched on its periphery so as to form splines, and a front clutchslider 96 is axially slidably but not relatively rotatably disposedaround the splines. The pinion shaft 95 is also notched on its peripheryso as to form splines, thereby being engaged with or disengaged from thefront clutch slider 96. A detent mechanism 21 is formed in the inputshaft 14 to define positions of the front clutch slider 96, i.e., anengage position where the front clutch slider 96 engages with the pinionshaft 95, and a disengage position where the front clutch slider 96disengages from the pinion shaft 95.

This clutch device 140 is interlocked with a later-discussed drive modechanging lever 130 through a linkage.

In the housing 88 of the front transaxle device 10, a differential 99 isprovided onto the left and right front axles 11 so as to differentiallyconnect the front axles 11 with each other. The differential 99 isconstructed similarly to the differential 89 of the middle transaxledevice 16. As shown in FIG. 2, the differential 99 comprises a hollowdifferential casing 45, a pinion shaft 46, pinions 49, and differentialside gears 48. The differential casing 45 is disposed coaxially with thefront axles 11 and rotatably supported by the housing 88. The pinionshaft 46 is disposed in the differential casing 45 so as to beintegrally rotatable with the differential casing 45. The pinions 49 aredisposed oppositely to each other and rotatably supported on the pinionshaft 46. Each of the differential side gears 48 is fixed onto an innerend of each of the front axles 11 so as to engage with both the pinions49.

An input gear 98, which is a spur gear to receive driving force for thedifferential 99, is fixed onto the differential casing 45.

Next, description will be given on a middle shaft 92 serving as a rotaryobject which intervenes between the differential 99 and the pinion shaft95.

The middle shaft 92 is disposed parallel to a rotational axis of thedifferential 99 (that is, a rotational axis of the differential casing45). A bevel gear 93 is fixed onto the middle shaft 92, and is engagedwith a bevel gear 97 fixedly provided on the pinion shaft 95.

The midway portion of the middle shaft 92 is notched on its periphery toform a reduction gear 91 as a spur gear. The reduction gear 91 isengaged with the input gear 98 of the differential 99.

The middle shaft 92 projects outwardly from the housing 88. A brakecasing 115 is fixedly provided onto the outside of the housing 88 so asto cover the projecting end portion of the middle shaft 92. A frontbrake device 100 as a multi-disc type brake is set up around theprojecting end portion of the middle shaft 92 between the brake casing115 and the housing 88.

In the front brake device 100, first friction discs 110 are axiallyslidably but not relatively rotatably provided onto the middle shaft 92.Second friction discs 111 are slidably but not relatively rotatablyengaged with the housing 88 of the front transaxle device 10. Each ofthe first friction discs 110 and each of the second friction discs 111are arranged alternately. A pressure member 113 is provided slidably andcoaxially to the middle shaft 92 for pressuring the multi-layeredfriction discs 110 and 111 against a receiving surface 112 formed at aninner wall of the housing 88. A piston 114 is provided integrally withthe pressure member 113 through a bolt 116.

The brake casing 115 projects outwardly and coaxially to the middleshaft 92 so as to form a cylindrical portion. The piston 114 is slidablyfitted in the cylindrical portion. Hydraulic fluid is to be tightlysupplied into a fluid chamber of the cylindrical portion of the brakecasing 115 which is formed between an utmost end surface of thecylindrical portion and the piston 114. By the hydraulic pressure of thefluid supplied into the fluid chamber, the piston 114 slides integrallywith the pressure member 113 so as to press the friction discs 110 and111 against one another, thereby braking the middle shaft 92.

As shown in FIG. 3 and others, there is formed a substantiallyring-shaped gap between an end surface of the piston 114 and thepressure member 113 along the inner peripheral surface of the brakecasing 115. In the gap are arranged a return spring 71, a collar 72, anda friction ring 73, which constitute an automatic gap alignmentmechanism 70 to keep a constant stroke of the piston 114 for the brakingoperation regardless of abrasive reduction of the friction discs 110 and111.

The return spring 71 is a ring-shaped spring, which is semicircular inits radial section. The major portion of the spring 71 is inserted intoa ring-like groove 74, which is formed on an end surface of the piston114 around the middle shaft 92 so as to face toward the discs 110 and111. An apex portion of the spring 71 in its sectionally semicircularshape projects toward the discs 110 and 111 so as to abut against thecollar 72. Thus, the spring 71 is sandwiched between the piston 114 andthe collar 72. The collar 72 is slidable on the inner peripheral surfaceof the cylindrical portion of the brake casing 115. The friction ring 73has outward biasing force in the radial direction and is fitted to aninner peripheral face of the brake casing 115. Therefore, the frictionring 73 is slidable on the inner peripheral surface of the cylindricalportion of the brake casing 115 against frictional resistance betweenthe friction ring 73 and the inner peripheral face of the brake casing115. This friction resistance applied onto the friction ring 73 islarger than the spring force of the return spring 71 and smaller thanthe hydraulic pressure applied on the piston 114.

Referring to FIG. 3, the friction discs 110 and 111 are new, i.e., theyare not worn. The total clearance between the friction discs 110 and 111is of a length A. Therefore, a stroke of length A is required for thepiston 114 to bring the friction discs 110 and 111 into contact with oneanother. An original amount of hydraulic fluid is filled in the fluidchamber so that the utmost end of the piston 114 is located at anoriginal brake-released position P. At this time, the return spring 71expands so as to generate a gap of the length A between the end surfaceof the piston 114 and the collar 72. The retaining ring 73 is sandwichedbetween the collar 72 and the pressure member 113.

For the braking operation of the front brake device 100, hydraulic fluidis supplied into the fluid chamber in the brake casing 115 so as to pushthe pressure member 113 toward friction discs 110 and 111. As shown inFIG. 4, when the piston 114 is moved at a stroke of length A, thefriction discs 110 and 111 are brought into engagement so that themiddle shaft 92 starts to be braked. During this stroke of the piston114, the return spring 71 is compressed between the collar 72 and thepiston 114 so as to absorb the pressure force of the piston 114, therebymaintaining the positions of the collar 72 and the friction ring 73.Therefore, the gap of the length A between the piston 114 and the collar72 is diminished, and a gap of the length A is generated between thefriction ring 73 and the pressure member 113.

For releasing the middle shaft 92 from its brake condition shown in FIG.4, fluid is drained from the fluid chamber in the cylindrical portion ofthe brake casing 115 so that the spring 71 returns to its expandedcondition, thereby locating the piston 114 at the originalbrake-releasing position P. The pressure member 113 follows the piston114, thereby disengaging the friction discs 110 and 111. Consequently,the front brake device 100 returns to the state as shown in FIG. 3.

Description will be given on the action of the automatic gap alignmentmechanism 70 corresponding to the abrasive reduction of the frictiondiscs 110 and 111 in accordance with FIGS. 5 to 7.

Referring to FIG. 5, friction discs 110′ and 111′ are abraded versionsof friction discs 110 and 111. The total abrasive reduction of the discs110′ and 111′ in the axial direction of the middle shaft 92 is of alength B. Therefore, even if the same amount of fluid as that in thesituation of FIG. 4 is supplied so as to move the piston 114 at a strokeof length A from its original brake-released position P, the frictiondiscs 110′ and 111′ are still disengaged. To bring the discs 110′ and111′ into engagement, the piston 114 requires an additional stroke oflength B. In other words, the piston 114 at the original brake-releasedposition P requires a stroke of lengths A+B for braking.

However, in the situation as shown in FIG. 5, the pressure member 113 isallowed to further move because of the additional clearance among thefriction discs 110′ and 111′ generated by their abrasion. Also, thecollar 72 abuts against the end surface of the piston 114 because of thecompression of the spring 71. Therefore, as shown in FIG. 6, increasedfluid is supplied so that the piston 114 is completely moved togetherwith the pressure member 113 at the stroke of length A+B from itsoriginal brake-released position P. During the movement of the piston114 and the pressure member 113, the end surface of the piston 114pushes the collar 72 together with the friction ring 73 against thefriction resistance between the friction ring 73 and the brake casing115. Therefore, the collar 72 and the friction ring 73 are shifted fromtheir original positions as shown in FIGS. 3 and 4.

Referring to FIG. 7, when the hydraulic pressure on the piston 114 isreleased, the friction ring 73 remains at its new position shifted fromits original position by its frictional resistance and the spring 71expands between the collar 72 and the piston 114. Therefore, the piston114 retreats only a stroke of length A by the expansion of the spring71. The pressure member 113 follows the retreating of the piston 114,thereby disengaging the friction discs 110′ and 111′. Consequently, anew brake-released position Q of the utmost end of the piston 114 isshifted from its original brake-release position P. The required strokeof the piston 114 in addition to the stroke of length A in the nextbraking operation of the front brake device 100 is just as much as thenew abrasive reduction of the discs 110 and 111.

Thus, on every braking action of the piston 114, the friction ring 73 isshifted so as to counter the additional clearance caused by the abrasionof the friction discs 110′ and 111′, thereby shifting the brake-releaseposition of the piston 114 toward the discs 110′ and 111′. Strictlyspeaking, the required stroke of the piston 114 in every brakingoperation is of the length A+B. However, in each braking operation, theadditional stroke of length B as much corresponding to the abrasivereduction of the friction discs 110′ and 111′ is extremely small,thereby being able to be ignored in measurement. Therefore, it may besaid that the stroke of the piston 114 required for every brakingoperation is substantially of the length A. In this meaning, the strokeof the piston 114 required for braking is kept constant regardless ofthe abrasive reduction of the friction discs 110′ and 111′.Consequently, the swift response of the front brake device 100 can bemaintained for a long period of use.

Referring to FIG. 8, in the front transaxle device 10′, a brake device100′ is disposed at the pinion shaft 95′, instead of the front brakedevice 100 disposed at the middle shaft 92. Description will be given onthis structure.

In the brake device 100′, first friction discs 110 are fit onto thepinion shaft 95′ such that the first friction discs 110 cannot rotatewith respect to the pinion shaft 95′. Second friction discs 111 areengaged with the housing 88′. Each of the first friction discs 110 andeach of the second friction discs 111 are arranged alternately. Thepiston 1119′ is provided to press the friction discs 110 and 111. Thepiston 119′ is formed into a ring-shape, and is fluid-tightly fittedwith a groove formed at an inner wall of the housing 88′ such that thepiston 119′ can be displaced in parallel with the pinion shaft 95′. Anoil path 121 is formed at the groove so as to apply hydraulic force ontoone end face of the piston 119′, thereby operating the piston 119′hydraulically. The oil path 121 is connected to an oil hydraulic circuit120 which will be described below.

In this structure, the piston 119′ is driven by the oil supplied fromthe oil hydraulic circuit 120 in such a direction as to project and topress the friction discs 110 and 111, thereby braking the pinion shaft95′ by friction.

Next, the structure in the multi-wheel-drive vehicle to operate thefront and rear brake devices 100 and 22 for braking by manipulation ofthe above-mentioned brake pedal will be described in accordance withFIG. 9.

The brake pedal 19 constituting the brake operating means in the presentembodiment is connected with the rear brake devices 22 and the frontbrake device 100 through the oil hydraulic circuit 120 shown in FIG. 9.The oil hydraulic circuit 120 comprises a master cylinder 101 todischarge oil for the brake devices 22 and 100, an oil tank 102 forsupplying oil to the master cylinder 101, a filter 103 for removingimpurities from the oil, an oil path 105 for leading oil from the mastercylinder 101 to the front and rear brake devices 100 and 22, and thelike.

The brake pedal 19 is supported rotatably, and an end of a rod 106 isconnected to the midway portion of the brake pedal 19. The other end ofthe rod 106 is fixed on a piston 107 disposed in the master cylinder101. A biasing spring 108, which also serves as a recovering spring forthe brake pedal 19, is disposed in the master cylinder 101.

The filter 103 and a manual valve 104 are disposed at a midway portionof the circuit for supplying oil from the oil tank 102 into the mastercylinder 101. The manual valve 104 is interlocked with the rod 106 suchthat the manual valve 104 opens the circuit when the brake pedal 19 isnot depressed, and that the manual valve 104 is switched by the rod 106and shuts the circuit when the brake pedal 19 is depressed therebypreventing oil from back-flowing in the circuit when the rod 106 pushesthe piston 107.

In this structure, when an operator depresses the brake pedal 19, thepiston 107 is pushed through the rod 106, and the master cylinder 101discharges the oil.

The discharged oil is led into the oil path 105 and is divided into twobranches. The oil in one branch runs to each of the rear brake devices22, thereby applying braking force onto the rear axles 8. The brakingforce is transmitted to the middle axles 25 connected to the rear axles8 through the drive shaft 17 and the like, thereby also braking themiddle axles 25. The oil in the other branch is led into the front brakedevice 100 to make the piston 114 in the front brake device 100 pressagainst friction discs 110 and 111, thereby applying braking force ontothe front axles 11 through the middle shaft 92.

Description will be given on the structure in the multi-wheel-drivevehicle to transmit the power from the engine 3 to the wheels 9, 12, and26.

As shown in FIG. 1, the transmission 13 provided in the rear transaxledevice 4 transmits the power from the engine 3 to the rear axles 8 todrive the rear wheels 9, and also transmits the power to the middletransaxle device 16 through the drive shaft 17 to drive the middlewheels 26 through the middle axles 25.

In other words, the power from the transmission 13 branches to the rearaxles 8 and the middle axles 25, thereby constantly driving the rearwheels 9 and the middle wheels 26 (four wheels in total).

Furthermore, the power, which is led from the engine 3 into the middletransaxle device 16, drives the input shaft 14 in the front transaxledevice 10 constantly through the transmission shaft 18.

The earlier-discussed clutch device 140 is disposed at the input shaft14. As shown in FIG. 9, the drive mode changing lever 130 is provided atthe appropriate portion of the vehicle to operate the clutch device 140,and the drive mode changing lever 130 is shiftable among a 4-wheel-driveposition and a 6-wheel-drive position (two positions in total). Thedrive mode changing lever 130 is linked with the front clutch slider 96in the clutch device 140 such that the clutch device 140 is engaged whenthe drive mode changing lever 130 is located at its 6-wheel-driveposition (as shown by ‘6WD’ position in FIG. 9) and that the clutchdevice 140 is disengaged when the drive mode changing lever 130 islocated at its 4-wheel-drive position (as shown by ‘4WD’ position inFIG. 9).

Therefore, when the drive mode changing lever 130 is located at its6-wheel-drive position, the clutch device 140 is engaged to drive thefront transaxle device 10 such that the front wheels 12 are driventhrough the front axles 11. Because the four wheels of the middle wheels26 and the rear wheels 9 are driven as described above at this time, thevehicle is put into 6-wheel-drive mode and all six wheels are driven.

On the other hand, when the drive mode changing lever 130 is located atits 4-wheel-drive position, the clutch device 140 is disengaged and thepower from the transmission 13 is shut off such that the front wheels 12are not driven. In this case, the vehicle is put into 4-wheel-drive modeand only the middle wheels 26 and the rear wheels 9, four wheels intotal, are driven.

The above-mentioned structure is an example and other embodiments may begiven. For instance, instead of the structure where an oil hydrauliccircuit 120 is used, a structure which will be described below mayapply.

An oil hydraulic circuit 120′ shown in FIG. 10, which is used in thismodification, is of the structure that a manual valve 150 which isswitchable among two positions is provided at the midway of a path forsupplying oil of the master cylinder 101 for the front brake device 100in the oil hydraulic circuit 120′ in the brake system.

A brake mode changing lever 155 serving as a brake mode changing meansis provided at the operator's section in the vehicle, and the manualvalve 150 is interlocked with the brake mode changing lever 155.

The brake mode changing lever 155 is shiftable according to anoperator's manipulation between a front-rear-brake position FRb and arear-brake position Rb.

When the brake mode changing lever 155 is located at itsfront-rear-brake position FRb, the manual valve 150 is opened. Thus,when the brake pedal 19 is depressed, oil from the master cylinder 101is supplied into both the rear brake devices 22 and front brake device100. In this case, the vehicle is put into front-rear-brake mode whereinthe rear and front brake devices 22 and 100 are put into action.

On the other hand, when the brake mode changing lever 155 is located atits rear-brake position Rb, the manual valve 150 is closed. Thus, whenthe brake pedal 19 is depressed, oil from the master cylinder 101 is notsupplied into the front brake device 100, but into the rear brakedevices 22. In this case, the vehicle is put into the rear-brake modewherein only the rear brake devices 22 are put into action.

Furthermore, the brake pedal 19 is linked with above-mentioned drivemode changing lever 130 through a linkage so as to make the drive modechanging lever 130 located at its 6-wheel-drive position when the brakepedal 19 is depressed.

The action of the above structure will be described. When the brake modechanging lever 155 is located at its rear-brake position Rb and thedrive mode changing lever 130 is located at its 4-wheel-drive position4WD, and when the brake pedal 19 is depressed, the manual valve 150 isclosed and only the rear brake devices 22 are put into action. However,because the drive mode changing lever 130 is switched into its6-wheel-drive position 6WD at the time when the brake pedal 19 isdepressed and the clutch device 140 linked with the drive mode changinglever 130 is engaged, the braking force which the rear brake devices 22apply onto the rear axles 8 and the middle axles 25 is also transmittedto the front axles 11 through the propeller shaft 18 and the like,thereby also braking the front axles 11.

Therefore, though the power from the engine 3 is transmitted to only therear axles 8 and the middle axles 25 such that four wheels are driven,braking force generated by only rear brake devices 22 is applied ontonot only the rear axles 8 and the middle axles 25 but also the frontaxles 11 such that all the six wheels can be braked.

In this structure, changing among 4-wheel-drive mode and 6-wheel-drivemode as the occasion arises is easy by engaging and disengaging theclutch device 140 by shifting the drive mode changing lever 130.

If the vehicle is put into the 4-wheel-drive mode and the brake pedal 19is depressed in the rear-brake mode, braking force generated by the rearbrake devices 22 is transmitted to the front axles 11 by the linkagebetween the brake pedal 19 and the clutch device 140. Though the frontbrake device 100 in the front transaxle device 10 is out of action, notonly the rear wheels 9 and the middle wheels 26 but also the frontwheels 12 are contributing to the braking of the vehicle. Thus, byputting the vehicle into the rear-brake mode, while good brakingperformance can be maintained, abrasion of the front brake device 100can be prevented.

Of course, the vehicle can be put into the front-rear-brake mode whichis effective when strong braking force is frequently desirable. In thismode, the front wheels 12 are braked by the front brake device 100 andthe rear wheels 9 and the middle wheels 26 are braked by the rear brakedevices 22. Good braking performance is achieved by applying brakingforce onto the rear wheels 9, the middle wheels 26, and the front wheels12 (all six wheels), and the rear brake devices 22 are protected fromoverload, such that heating and abrasion can be minimized.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form may be changed in the details ofconstruction and the combination and arrangement of parts may beresorted without departing from the spirit and the scope of theinvention as hereinafter claimed.

For example, the front transaxle device in the present invention canapply not only to a six-wheel-drive vehicle as described in aboveembodiment but also to a multi-wheel-drive vehicle wherein eight or morewheels are driven.

1. A vehicle comprising: a first drive wheel; a second drive wheel; anengine disposed between the first and second drive wheels; a firsttransaxle supporting the first drive wheel, the first transaxleincluding a first input shaft extending laterally with respect to thevehicle; a second transaxle supporting the second drive wheel, thesecond transaxle including a second input shaft disposed at asubstantially lateral central portion of the vehicle and extendingtoward the first transaxle; a belt stepless transmission disposed on oneof left and right sides of the first transaxle and drivingly interposedbetween the engine and the first input shaft; and a power transmissionmember drivingly interposed between the first transaxle and the secondinput shaft, the power transmission member including a firsttransmission shaft extending from the first transaxle in thesubstantially exact fore-and-aft direction of the vehicle and disposedon the other of the right and left sides of the first transaxle, and asecond transmission shaft extending laterally slantwise when viewed inplan and interposed between the first transmission shaft and the secondinput shaft.
 2. The vehicle according to claim 1, wherein the secondtransaxle further includes a clutch drivingly interposed between thesecond input shaft and the second drive wheel.
 3. The vehicle accordingto claim 1, wherein the second transmission shaft is provided with atleast two universal joints, one connected to each of the firsttransmission shaft and the second input shaft.
 4. A vehicle comprising:a first drive wheel; a second drive wheel; an engine disposed betweenthe first and second drive wheels; a first transaxle supporting thefirst drive wheel, the first transaxle including a first input shaftextending laterally with respect to the vehicle, and a travelingdirection changing device for changing forward/backward travelingdirection of the vehicle; a second transaxle supporting the second drivewheel, the second transaxle including a second input shaft disposed at asubstantially lateral central portion of the vehicle and extendingtoward the first transaxle; a belt stepless transmission disposed on oneof the left and right sides of the first transaxle and drivinglyinterposed between the engine and the first input shaft; and a powertransmission member drivingly interposed between the first transaxle andthe second input shaft, the power transmission member including a firsttransmission shaft extending from a downstream portion of the travelingdirection changing device in the first transaxle in the substantiallyexact fore-and-aft direction of the vehicle and disposed on the other ofthe right and left sides of the first transaxle, and a secondtransmission shaft extending laterally slantwise when viewed in plan andinterposed between the first transmission shaft and the second inputshaft.
 5. The vehicle according to claim 4, wherein the second transaxlefurther includes a clutch drivingly interposed between the second inputshaft and the second drive wheel.
 6. The vehicle according to claim 4,wherein the second transmission shaft is provided with at least twouniversal joints, one connected to each of the first transmission shaftand the second input shaft.